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View Full Version : 4.0 Head swap on 4.2



UPJ Wheeler
10-26-2009, 09:02 PM
Well, here it is finally, Ive been busy as all hell with my last year of school.

I was tired on only being able to do 45mph up hills, and having zero passing power on the highway. I had no complaints about the 4.2's performance in the woods, this swap was purely for better on road performance.

I'd also like to say that before doing this project I had ZERO experience doing any kind of engine or head gasket work. It's easy as pie. Took me 2 full days to do it working by myself just taking my time, and about 6 hours of that was doing research and making phone calls, and driving to get head bolts.

Started out with a 7130 casting head from a ZJ 4.0, and had a friend of a friend who built racing motors redo the head for me on the cheap. The price of the head work was right,and I'm pretty sure that It got all new valve guides, seals, springs, ect.... The rebuilt head sat on a shelf for 2 years until I had time and the extra cash to finish the swap.

My old 4.2 had 18,000 miles since a complete rebuild when the new head went on.

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap005.jpg


Getting the 4.0 head prepped involved filling in some water jacket holes using the packing peanut and epoxy method. Lots of people frown upon this method and say that the jackets should be welded and the head decked. There have been cases where the epoxy method did not work and there was sufficient coolant leakage. I researched and found that most of these cases failed due to the use of a MOPAR riveted head gasket. The rivets do not allow the head to properly seat on the block, and this is the primary cause of the leakage.

There were plenty of chevy motors that had water jackets blocked by the head gasket alone. This set up has the head gasket and epoxy sealing the water jackets that are not used. When done correctly, other people have put on 60,000 miles with no issues.

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap007.jpg

http://www.off-road.com/jeep/tech/engine/40headconv/Diagram3.jpg

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap010.jpg


Old head removed as an assembly with the intake and exhaust still attached

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap014.jpg

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap013.jpg

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap024.jpg

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap018.jpg

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap021.jpg

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap015.jpg

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap017.jpg


New head with Stainless steel header ($60 off of one of the Forums), and 4.2 intake and carb (will be installing TBI as soon as funds and time allow)

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap008.jpg

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap026.jpg

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap025.jpg



When I got into the motor, I found that I have one of the earlier 4.2's with 1/2" head bolts, so I didnt need to use the 7/16" spacers that I bought. (These are for sale if someone wants to get into their own swap!) I ran into a problem with the passenger side head bolts from the 4.2 being too long to reuse, and the Dealer was the only place I could get the Correct ones. Ended up to drive to two different Jeep dealers to get 7 of them at 10 bux a pop, OUCH!

http://i50.photobucket.com/albums/f318/UPJwheeler/Head%20Swap/40headswap028.jpg



I got it all figured out and bolted down using factory torque specs.

Had to do some drilling to make the power steering bracket work. I was really truckn at this point and forgot to stop and take pictures. Sorry Guys.

Finished it off with new plugs, reconnected all of the electrical and vacuum lines, and she fired right up!!!!

That bitch was LOUD coming right out of the header! Drove it a few miles down the road to the local speed shop for the owner to put a new 2.25" exhaust with a high flow cat and nock-off flow master. Sounds SWEET!!!



Over all Impressions after 1,000 miles....

-Better Oil Pressure >> Seems kinda odd, but I was running 30 psi at start up and 10 psi at temp before, and now with the 4.0 head start up is around 60psi, and at temp between 35-40psi.

-Can do 70 MPH coming up the mountain on the PA turnpike from donegal to sommerset

-no problem having the power to pass people on the highway

-Lost some low end torque. >>> only noticeable in the woods. I used to be able to put it in first gear low range and let it idle. Now it wont idle over obstacles, I've got to give it a feather of throttle. Cheenin and I talked about it, and deduced that the larger intake ports require less air velocity to move the same volume of air per second comparatively than with the constrictive 4.2 head intake ports.



-BURNS OIL >> WTF!!!! the only thing I can figure is that the valve seals dry rotted while it sat on the work bench, Ill replace them if it gets too bad.

-still havnt calculated MPG, but it seems about the same, net long highway trip ill check it out.



All in all its DEFINITELY worth the time and cash for the improvement in drive ability!!!!!

UPJ Wheeler
01-06-2010, 09:18 PM
just for an update after 2000 miles...

got 15.5 MPG driving from pgh to j-town yesterday doing 50-55mph on the snowy highways, and goofn around and gettn stuck in 3.5 feet of snow in my buddys front yard for an hour or so. It runs smoother and stronger than it ever did with the original head, and will start without giving it any gas after its warm (always had to give it gas with the old one)

Still burnin oil, was planning on replacing valve seals over christmas break, but just flat ran out of time... try again spring break...

here's a good example of the smokn that it does... never burned an ounce before the head swap
http://i50.photobucket.com/albums/f318/UPJwheeler/Doe%20Vally%20Pig%20Roast%208-30-09/IMG_1822.jpg